CHICAGO — Another dominant lefty made sure the Royals’ post-break blues continued Monday.

Chris Sale pitched seven effective innings in his first outing since his All-Star appearance and Adam Dunn had two RBIs and scored a run to lead the Chicago White Sox to a 3-1 victory over the slumping Royals, who are now 0-4 since the All-Star break.

Sale (9-1) wasn’t at his best, allowing seven hits and a walk in seven innings, but he worked out of jams in the fourth and sixth innings. He struck out eight and now has allowed three runs or less in 14 of his 15 starts this season. Jake Petricka pitched the ninth for his fourth save.

Dunn went 1 for 2 with a pair of walks as the White Sox won for the fourth time in six games.

Danny Valencia went 1 for 2 with an RBI for Kansas City, which has dropped four straight and seven of eight. The Royals had a team meeting before the game, but couldn’t turn around their fortunes as they dropped two games below .500 (48-50).

Royals starter Jeremy Guthrie (5-9) gave up three runs on five hits in six innings to get the loss. He had been 4-0 against the White Sox with the Royals before Monday.

“The first inning he really grinded,” Royals manager Ned Yost said, “but the second inning he settled down and started making really quality pitches.”

The White Sox took a 2-0 lead in the first inning as the first four batters reached base. Adam Eaton singled, Alexei Ramirez was hit by a pitch and Jose Abreu reached on an error by Valencia at third base to load the bases.

Dunn then singled up the middle against the shift — essentially hitting the ball to the normal shortstop position — to score both Eaton and Ramirez.

The Royals trimmed the lead in half in the fourth. Alex Gordon singled with one out, stole second and then scored on a two-out single by Valencia. The next batter, Alcides Escobar, doubled down the left-field line and it appeared the score would be tied, but Valencia was nailed at the plate as left-fielder Alejandro De Aza and Ramirez got the ball to catcher Tyler Flowers for the putout to end the inning.

The White Sox regained the two-run edge in the sixth as Dunn scored on a sacrifice fly by Gordon Beckham to make it 3-1.

The Royals threatened in the top of the sixth inning, when Salvador Perez and Billy Butler reached base with one out. But Valencia could not move the runners, striking out swinging on a 3-2 pitch, and Escobar struck out looking ot end the inning.

Yost said he would have liked to have seen a better plate appearance from Valencia in that situation.

“Of course,” Yost said. “You don’t want to swing at a ball at your shoulders, especially a 3-2 pitch that is going to load the bases.”

The Royals fell 71/2 games behind the Detroit Tigers in the American League Central and four games behind the Seattle Mariners for the second wild card spot.

Still, Yost said he thought the team showed much better effort Monday than it did against Jon Lester and the Boston Red Sox in Sunday’s 6-0 defeat, which prompted the team meeting.

“Yes, I’d have to say yes to that,” Yost said. “I thought there was more energy, we had better at-bats. I thought it was better today.”

■ Royals 1B Eric Hosmer was scratched about an hour before game time with a right hand contusion. He was hit on the hand with a pitch by Lester in Sunday’s game at Fenway Park.

■ White Sox pitching coach Don Cooper is suffering from vertigo and missed a second straight game on Monday. Bullpen coach Bobby Thigpen took his place.

■ Perez was back in the lineup after sitting out Sunday with a groin strain. He originally was going to catch but switched to DH when Hosmer was scratched. “He feels much better,” Yost said. “He’s not a speed demon to begin with. It’s still probably going to affect him a little bit running, but he can catch and swing and do everything else.”

■ Abreu doubled in the seventh to extend his hitting streak to 12 games.

■ LHP Bruce Chen (1-2) takes on Scott Carroll (4-5) in the second game of the series.